In general, powder compacting apparatuses are used for instance in the conventional metallurgy industries in which a basic iron powder is blended with a copper powder, a graphite powder or the like alloy element to prepare a composition. Usually added to this composition is a lubricant such as zinc stearate, lead stearate or the like, to provide a mixed powder that will then be compacted in a press mold. Powder metallurgy is a process for producing for example such an iron-based compacted powder pieces, and in the atomic power industries the mold is disposed in a glove box so as to produce such pieces as nuclear fuel pellets.
Presses widely used in this field comprise each two or more punches for a mold.
One of the prior art powder compacting apparatuses is disclosed in the Japan Patent Laying-Open Gazette No. H.9-253896 and shown in “FIG. 1” thereof (—FIG. 7—herein). This apparatus comprises a punch holder for attaching an upper punch to a top plate, a die plate for holding a die, and a bottom plate to which a lower punch is secured. The upper and lower punches are strongly urged towards each other to compress a powder mixture and compact it into a consolidated piece.
Now, FIG. 7 will be referred to in detail for description of the prior art type of powder compacting apparatuses.
This prior art proposes a die device for incorporation into a powder compacting apparatus. The die device comprises an upper punch 113 held in place by an upper holder 112, that is bolted to the lower face of a top plate 110. A die 121 fitted downwards in a die plate 123 is fixed therein by a die retainer 122 bolted thereto. A die plate supporter 126 is disposed below and adjacent to the lower face of die plate 123. A pair of guide posts 114 depend from opposite side ends of the top plate 110. These posts are loosely extend through corresponding holes formed in the die plate 123. Beatings secured in the supporter 126 hold the lower end portions of such guide posts 114 in a freely rotating engagement with said supporter. The die 121 has a central bore fitting on the top end of a lower punch 131, that can reciprocate up and down relative to this die 121. A lower holder 132 is bolted to a base plate 140 so as to retain thereon the lower punch 131. A pair of upright guide rods 160 penetrate the opposite side regions of said base plate 140.
In operation, an amount of powder will be placed in the die 121, and then the top plate 110 will be lowered along the guide posts 114 so that the upper punch 113 descends towards the die 121. On the other hand, the base plate 140 will be raised along the guide rods 160, thus driving the lower punch 131 upwardly towards the die 121. Those upper and lower punches 113 and 131 cooperate with each other to press the powder between them, thereby compacting it into a consolidated piece.
When setting this apparatus ready to operate, the upper end of lower punch 131 will be positioned at first to fit in the die 121. This die will then engage the die plate 123, before the retainer 122 is placed onto the die and bolted downwards to this die plate. The lower holder 132 restraining the lower punch 131 from sideways movement will be bolted downwards to the base plate 140 so as to fix thereon the lower punch. Subsequently, the lower end of upper punch 113 will be fitted in die 121, before temporarily lowering the top plate 110. Next, the upper holder 112 will be positioned correct relative to this plate by upwardly screwing some bolts. As the final step, the top plate 110 will be retracted upwards in order to tightly fasten those bolts for firmly fixing the upper punch 113.
In the powder compacting apparatus summarized above, many bolts are used around the die 121 in order that the retainer 122 urges downwards this die within the die plate 123. Thus, very intricate and time-consuming works are necessary when mounting and dismounting the die 121.
As also noted above, the upper punch 113 has to preliminarily fit in the die 121 to be aligned therewith. Thus, many further bolts inserted upwards through the upper holder 112 will be allowed to loosely engage with the top plate 110. Subsequently, the top plate will be lifted to tightly fasten the bolts and firmly secure the upper punch 113 in position. Due to almost impossible visual inspection of the positions of those bolts and bolt holes receiving them, the upper holder 112 is not easy to fix. All the works to bolt this holder 112 may alternatively be done after having raised the top plate 110. In this case, it will however be more difficult to precisely align the upper punch 113 with the die 121, also failing to smoothly attach and quickly fasten those bolts.
The upper punch 113 should be protected from damage when it is driven into a smooth alignment with the die 121. For this purpose, a manually operable mold changer may be necessary for slowly raising and lowering the upper punch. Such a mold changer will be located apart from the main body of a powder compacting apparatus. Therefore, a set of dies and relevant members therefor must move fore and aft between such a changer and the apparatus.